It's not rocket science, but if you need a way to keep plastic garbage bags around and you have a leftover piece of PVC pipe you can make a simple bag dispenser by cutting a slot in the side of the pipe and mounting holes on the back.

To use just slide in a roll of bags and pull one out through the slot. PVC project weblog PVC Workshop used a jigsaw to cut out the bag opening, but I'm pretty sure I could get the same cut done by drilling a hole and using the saw on my Swiss Army Knife.